Problem: Solve for $a$ : $27 + a = 26$
Subtract $27$ from both sides: $ \begin{eqnarray} \\ 27 + a &=& 26 \\ \\ {-27} && {-27} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{27 + a} &\hphantom{=}& \hphantom{26} \\ a &=& 26 {- 27} \\ \end{eqnarray} $ Simplify. $ a = -1$